This invention relates generally to apparatus for atomizing fuel supplied to the combustion chamber of an engine or furnace, and more particularly to a fuel-atomizing unit adapted to be interposed between the carburetor and intake manifold of an internal-combustion engine and serving to convert an incoming fuel-air mixture into a mist which is heated to a level conducive to complete combustion in the chamber.
The modern era is marked by a growing concern with the inadequate supply of fuel and the rising cost thereof, as well as with the ecological damage resulting from the emission of pollutants from fuel-burning engines and furnaces. Hence while there is a strong international interest in reducing pollutants emanating from automobiles and oil burners, there is at the same time a great desire to effect economies in fuel consumption to conserve the available fuel.
Many expedients heretofore suggested to control pollution have been at the expense of fuel economy. For example, catalytic converters which are designed for installation in the exhaust of a vehicle to cut down the emission of pollutants have an adverse effect on the efficiency of the engine and cause the engine to burn more gasoline. Thus whatever is gained in ecological terms is contradicted by significant economic losses.
In an internal combustion engine, the pollutants are constituted by oxides of nitrogen, unburned hydrocarbons and carbon monoxide. But it is not only the emission from the engine exhaust into the atmosphere which creates an ecological problem, for the emitted substances give rise to chemical reactions in the atmosphere when radiant energy is supplied thereto by the sun. Thus the smog now encountered in many major cities is largely the result of photochemical reactions involving unburned hydrocarbons from automobile exhausts. These unburned hydrocarbons are also responsible for inefficient engine operation, in that carbon deposits are formed on the walls of combustion chambers.
Thus with existing internal-combustion engines, a measurable portion of the fuel supplied thereto remains unburned and is discharged. This not only results in an uneconomical engine operation, but it also contaminates the atmosphere.
Attempts have heretofore been made to interpose an atomizer between the carburetor and the intake of the engine to insure complete combustion of the fuel. For example, U.S. Pat. No. 3,544,290 discloses a unit in the form of a strainer for the fuel-air mixture operating in conjunction with a vibrator to agitate the mixture in order to effect atomization thereof. Similar attempts to homogenize the air-gas mixture are disclosed in U.S. Pat. Nos. 1,260,699 and 1,035,614. In U.S. Pat. Nos. 3,899,949 and 1,380,824, use is made of screen members in conjunction with heaters to vaporize the fuel. But in all instances, the arrangements disclosed in the prior art possess certain practical drawbacks which have militated against their general commercial acceptance.
In my above-identified copending application (to be granted as U.S. Pat. No. 4,020,812 on May 3, 1977), there is disclosed an improved atomizing unit serving to homogenize and heat the fuel mixture fed into the combustion chamber of an engine or any fuel burner so that complete combustion thereof takes place, thereby making maximum use of the available fuel and minimizing the emission of unburned fuel constituents.
In the unit disclosed in my copending application, the entire disclosure of which is incorporated herein by reference, the unit is designed to be interposed in a conduit feeding a relatively cold mixture of fuel droplets dispersed in an air stream to a combustion chamber for ignition therein. The unit includes a pair of parallel mesh screens having an electrical heating element in the space therebetween to define a zone which restricts the flow of the air-fuel mixture, the screen dissecting the droplets to develop in the output of a unit a fog-like suspension of atomized fuel particles in air.
The heating element is energized to heat the zone to a temperature level which in free air exceeds 500.degree. F., the heat causing the fog in the output of the unit to attain a temperature level of about 90.degree. F. to promote vaporization thereof before it enters the combustion chamber.
The screens and the heater are held in spaced relation within a stack of electrically insulating heat-resistant gaskets having an opening therein for the passage of the mixture, the stack including a metal gasket acting as a heat sink to prevent excessive heating that might otherwise burn out the unit.
In order to avoid leakage of the air-fuel mixture from the unit, the gaskets in the stack are laminated together by a bonding agent. However, because of chemical reactions resulting from the presence of gasoline and the heat involved, some degree of delamination is experienced with prolonged use of the unit, and leaks are developed which degrade the efficiency of the carburetion system. Moreover, a unit which requires a stack of gaskets which must be interlaminated is relatively inexpensive to manufacture.
Another problem encountered with a unit of the type disclosed in my prior application relates to the insulation of the heater wire; for the inorganic ceramic coating thereon is relatively brittle. As a consequence, when the heater wire is subjected to vibratory or shock forces, the insulation may crack and break off, and the uninsulated wire may then make contact with the wire mesh screen and short out the heater.